1. Field of the Invention
The invention relates to a pivotable printing-form changing device for simply and rapidly changing printing forms to be fed to and removed from a cylinder, and to a method for changing printing forms.
The published European Patent Document EP 0 678 382 A1 discloses a device for replacing printing forms for rotary printing machines, especially in web-fed rotary printing machines for printing both sides of a web. Provided on these machines is at least one printing unit that accommodates at least one printing mechanism and a printing-form cylinder taking up the ends of a printing form wound around the surface of the cylinder. This cylinder has clamping devices within a gap and has assigned thereto a discharge device for the printing form that has been released from the plate cylinder and is to be changed, and a feed device for printing forms or plates which are to be newly affixed to the surface of the form cylinder. To the printing-form cylinder of a lower printing mechanism of a printing unit, there is assigned both a pivotable holder and feeder for new printing forms, and a pivotable holder for the printing forms to be removed from the form cylinder, the latter holder serving to pick up and release the printing forms in a downwardly hanging attitude.
The published European Patent Document EP 0 678 383 A1 is concerned with a device for exchanging printing plates in rotary printing machines. A printing unit of a rotary printing machine includes a printing-form or plate cylinder that takes up the two ends of a printing form or plate in a gap, the surface of the printing form or plate being wound around the cylinder, a device accommodating the printing form, that is located at the then time on the printing-form cylinder, after the printing form has been released by the clamping devices of the printing-form cylinder, as well as a device for feeding a new printing form to the printing-form cylinder. The latter device is distinguished by the fact that, at a slight distance from the outer surface of the printing-form cylinder, horizontally movable holding elements fix the leading edge of a printing form to be fed, until a remotely-controlled, engageable pivotable holder throws the leading edge of the printing form to be fed onto the outer surface of the printing-form cylinder.
In the two aforementioned constructions from the respective published German Patent Documents EP 678 383 A1 and EP 678 382 A1, the printing forms slide over suction cups during the clamping movement thereof on the form cylinder. This requires the rear surface of the printing forms which are to be drawn onto the cylinder to have a lubricating film provided thereon. Because this remains an activity that is largely performed manually, however, the lubricating film is not applied uniformly over the rear of the form. Furthermore, after a time, the lubricant is deposited or transferred onto the circumferential surface of the form cylinder and imparts sliding properties thereto which are undesirable and, moreover, necessitate frequent cleaning of the circumferential surface of the form cylinder. Furthermore, the suction cups required here for fixing the rear of the printing forms need an adequate vacuum to ensure the correct functioning of the suction cups. This embodiment calls for a large number of vacuum pumps and, therefore, requires a considerable outlay or expense to provide the vacuum.
The published European Patent Document EP 0 712 725 A2 is concerned with a rolling element for pressing a flexible printing form onto the form cylinder. The rolling element serves to press a flexible printing form onto the form cylinder of a printing unit of a rotary printing machine during a printing-form change. The rolling element includes a number of rollers which are arranged along the circumference of the form cylinder and can be set individually onto the latter. One or more first rollers can be set onto the form cylinder during the mounting of the printing form, and one or more second rollers can be set onto the form cylinder during the removal of the printing form, in the region of the printing form.
The published European Patent Document EP 0 667 237 A1 has disclosed an automated printing-form changing device. In this device for automatically changing printing forms in a printing machine, conceived for a sheet-fed printing machine, a printing form to be fed to the form cylinder is conveyed between driven transport rollers and backpressure rollers. The correspondingly driven transport rollers and the corresponding backpressure rollers are mounted so as to be movable in the axial direction of the form cylinder.
Finally, reference should be made to the published German Patent Document DE 39 40 795 C2 which discloses a method and a device for automatically feeding and removing a printing form, respectively. On a rotary printing machine, the start of the printing form and the end of the printing form are fixed on the form cylinder. The printing form is placed in a storage chamber in a printing form feed and removal device, respectively. The form cylinder is then rotated into a printing form feed position, and the printing form is fed to the clamping device of the form cylinder. In order to remove the printing form, the form cylinder is rotated into a form loosening position, and the clamping element for gripping the printing form end is opened. The form cylinder is then rotated backwards into the printing form feed position, and a clamping flap for gripping a printing form start is opened. The printing form is fed to the storage chamber of the printing form feed and removal device, respectively.
In the heretofore known devices of this general type, not just the leading edge alone, but both the leading edge and the trailing edge of a respectively new printing form are inserted into the cylinder gap. A separate pressure roller is required for this and, during the operation wherein the printing forms are clamped onto the form cylinder, a throw-on or retaining force is necessary, i.e., the delivery rollers, the pressure rollers, and so forth, have to be provided with controllable drives.
In view of the foregoing prior art, it is an object of the invention to provide a pivotable printing-form changing device configured for respectively feeding printing forms to a form cylinder and removing printing forms from a form cylinder while avoiding any requirement for additional backpressure, pressure or transport rollers.
With the foregoing and other objects in view, there is provided, in accordance with a first aspect of the invention, a device for changing printing forms on form cylinders of rotary printing machines, having a pivotable surface for guiding the printing forms to be changed, which are grippable at an underside thereof, comprising a pivotable printing-form table to which a separately actuatable contact member is assigned, the contact member being throwable onto a surface of a printing form disposed on the printing-form table for positioning the printing form in any selective position.
In accordance with another feature of the invention, the changing device includes a lever extension, the printing-form table and the lever extension being pivotable about a common pivot axis.
In accordance with a further feature of the invention, the changing device includes a separate actuating unit assigned to the printing-form table.
In accordance with an added feature of the invention, the changing device includes an independent actuating unit assigned to the separately actuatable contact member.
In accordance with an additional feature of the invention, the changing device includes separate actuating units, respectively, assigned to the printing-form table and to the contact member, respectively, at least one of the actuating units being constructed as a piston/cylinder unit.
In accordance with an alternative feature of the invention, the changing device includes separate actuating units, respectively, assigned to the printing-form table and to the contact member, respectively, at least one of the actuating units being constructed as an electromotive drive.
In accordance with yet another feature of the invention, the printing-form table is formed with an insert.
In accordance with yet a further feature of the invention, the insert has a flat surface.
In accordance with an alternative feature of the invention, the insert has a curved surface.
In accordance with yet an added feature of the invention, the contact member is a freely rotatable roller.
In accordance with an alternative feature of the invention, the contact member is a driven roller.
In accordance with yet an additional feature of the invention, the contact member is a roller having a yieldable surface.
In accordance with still another feature of the invention, the contact member is a roller subjectible to a pressure-medium loading.
In accordance with still a further feature of the invention, the insert is a component extending continuously over the width of the form cylinder.
In accordance with still an added feature of the invention, the insert comprises a plurality of components arranged at spaced intervals from one another over the width of the form cylinder.
In accordance with another aspect of the invention, there is provided a method for changing printing forms, which comprises exclusively feeding printing forms to a form cylinder.
In accordance with a further aspect of the invention, there is provided a method for changing printing forms, which comprises expressly removing printing forms from a form cylinder.
In accordance with a concomitant aspect of the invention, there is provided a printing unit of a rotary printing machine including a device for changing printing forms on form cylinders of the rotary printing machine, the changing device having a pivotable surface for guiding the printing forms to be changed, which are grippable at an underside thereof, comprising a pivotable printing-form table to which a separately actuatable contact member is assigned, the contact member being throwable onto a surface of a printing form disposed on the printing-form table for positioning the printing form in any selective position.
The changing device according to the invention is associated with a number of advantages. By a simple pivoting movement, the printing form can be thrown onto the outer surface of the form cylinder so that no further pressure rollers are needed for drawing the printing form onto the cylinder. Moreover, the application of a lubricating film to the underside of the printing form in order to seal off suction elements can be dispensed with completely, due to the fact that the printing form now adheres to the feed device only because of the frictional force and can be brought by the latter into any draw-on position or any position required for removal.
In a further refinement of the idea upon which the invention is based, the printing-form table and a lever extension, to which the contact member is connected, are movable about a common pivot axis. As a result, when there a printing form is located on the printing-form table, assurance is provided that the form is moved together with the pivotable printing-form table, so that the printing form can remain at all times in a defined attitude. Both the printing-form table and the separately actuatable contact member have an independent actuating unit, respectively, assigned thereto, it being possible for the throwing of the contact member onto the printing form to be varied as required. In addition to configuring the actuating unit as a piston/cylinder unit, the actuating units can also be formed as electromotive drives. The printing-form table is provided with an insert that is able to be incorporated into the table so that the latter remains flat; equally possible is a convex curvature of the insert, in order to stiffen the flat printing form by deformation. The contact member can be constructed, for example, as a freely rotatable roller that rotates freely on the lever extension and, when the printing form is being drawn onto the surface of the form cylinder, rolls on the surface of the printing form. Instead of being a freely rotatable roller, the contact member may be a driven roller. If the contact member is formed as a roller, the roller surface is preferably formed on a resilient, yieldable material; equally well, the contact member may be formed of a tube-like element loadable by or subjectible to a pressure medium loading.
The insert embedded or mortised in the pivotable printing-form table can be a continuous component extending over the width of the form cylinder. In addition to such a single-piece or unipartite construction, it is also possible for a number of insert components to be distributed over the width of the form cylinder, arranged at spaced intervals from one another. The device according to the invention can be used in such a way that it serves exclusively to feed printing forms. The device according to the invention can further be provided to remove the printing forms. For each printing unit, two of the devices according to the invention can be used for feeding the printing form, and for removing the latter from the form cylinder again; in this configuration, the device feeding the printing form can access a magazine with prepared printing forms, while the printing forms which have already been used can be deposited in a separate magazine by the further device according to the invention.
Other features which are considered as characteristic for the invention are set forth in the appended claims.
Although the invention is illustrated and described herein as embodied in a pivotable printing-form changing device, and a method for changing printing forms, it is nevertheless not intended to be limited to the details shown, since various modifications and structural changes may be made therein without departing from the spirit of the invention and within the scope and range of equivalents of the claims.
The construction and method of operation of the invention, however, together with additional objects and advantages thereof will be best understood from the following description of specific embodiments when read in connection with the accompanying drawings, wherein: